Mr. Brian Latouf
Director, Safety Regulations & Consumer Information
General Motors North America
Mail Code: 480 111 E18
30200 Mound Road
Warren, MI 48090-9010
Dear Mr. Latouf:
This responds to your request for an interpretation of Federal Motor Vehicle Safety Standard No. 126, Electronic Stability Control Systems. You asked that we confirm your interpretations of four different aspects of the new electronic stability control (ESC) systems rule. Based on the information you provided and our analysis below, we generally agree with your suggested interpretations. Our analysis is divided into four parts as per your questions.
Whether ESC must operate during the ESC sensor initialization period
You first asked us to confirm that FMVSS 126 does not require ESC to be operational during the ESC sensor initialization period. You noted that subparagraph (6) of the definition of ESC and S5.1.2 of FMVSS No. 126 both indicate that ESC systems must be operational at vehicle speeds of 15 km/h and above. However, you argued that different vehicles and ESC systems have different diagnostic and sensor initialization periods, requiring different inputs, after the vehicle is first started, and that it is possible that on some vehicles sensor initialization might not be completed before the vehicle speed reaches 15 km/h. Therefore, you asked that we confirm that the 15 km/h operational requirement prescribed in the definition of ESC and in S5.1.2 applies after the system diagnostic and sensor initialization is completed.
We are able to confirm your interpretation that the 15 km/h low speed threshold prescribed in the definition of ESC and in S5.1.2 applies after the system diagnostic and sensor initialization is completed. We recognize that an ESC system may not be fully operational until after it completes system diagnostic and sensor initialization. While not directly applicable to the 15 km/h operational requirement, we note that it was in recognition of the fact that ESC systems may require a diagnostic and sensor initialization period that we included a diagnostic procedure in S7.10.2 of FMVSS No. 126, as part of the test procedure for evaluating the ESC systems ability to detect malfunctions. An ESC system may not be able to detect a malfunction, or the absence of a malfunction, if it is not yet fully operational, so we included this diagnostic and initialization procedure as part of that test procedure.
Whether compliance with the requirements prescribed in S5.3 and its subparagraphs is determined by testing the vehicle in accordance with S7.10
You next asked us to confirm that the performance requirements of S5.3 of FMVSS No. 126 apply specifically when evaluated according to the procedures of S7.10. You specifically asked about S5.3.3. That paragraph states, in relevant part, that the ESC malfunction telltale must illuminate only when a malfunction(s) exists and must remain continuously illuminated under the conditions specified in S5.3 for as long as the malfunction(s) exists, whenever the ignition locking system is in the On (Run) position. S7.10, which provides a procedure for testing the malfunction telltale, states that the telltale is to illuminate within two minutes of obtaining a specified speed (S7.10.2). You argued that While a possible reading of S5.3.3 is that it requires the malfunction telltale to illuminate instantaneously with the occurrence of the fault, this is neither practicable nor consistent with the test procedure specified in S7.10.
We note that the introductory paragraph of S5, Requirements, states that each vehicle must be equipped with an ESC system that meets the requirements specified in S5 under the test conditions specified in S6 and the test procedures specified in S7 of this standard. Thus, as a general matter, compliance with the requirements prescribed in S5 (of which S5.3 is a part) is evaluated under the test procedures specified in S7 (of which S7.10 is a part).
In terms of providing an interpretation, we will limit our interpretation to the specific issue you asked about, whether S5.3.3 has the effect of requiring the ESC malfunction telltale to illuminate instantaneously with the occurrence with the fault. The answer is no. We recognize that it may not be practicable for a malfunction telltale to illuminate instantaneously with the occurrence of a fault. As you noted, S7.10 provides a test procedure for evaluating ESC malfunction detection. After one or more malfunctions is simulated, a vehicle is subjected to a specified driving protocol. See S7.10.2. Under the procedure, verification is made that the telltale is illuminated within two minutes of the vehicle obtaining a specified speed. This procedure accommodates the need for system diagnostic and sensor initialization (discussed above) and the fact that a malfunction telltale may not illuminate instantaneously with the occurrence of a fault.
Whether FMVSS No. 126 allows the same test protocol to clear ESC faults (and extinguish the malfunction telltale) as that which is specified to detect ESC faults (and illuminate the malfunction telltale)
You next asked us to confirm that the driving protocol of S7.10.2 is permissible for purposes of verifying that the ESC malfunction has been cleared under S7.10.4, which does not contain any specific protocol. You argued that As ESC systems are generally designed, the diagnostic procedures required to detect a fault (e.g., vehicle speed, steering-wheel inputs, etc.) are also required to determine that the fault has been cleared. Thus, not all ESC systems would necessarily be able to clear a fault just by restarting the vehicle, without any diagnostic procedures.
We recognize that just as a diagnostic procedure may be necessary for an ESC system to detect a fault, it may also be necessary to determine that the fault has been cleared. The lack of an identical driving protocol in S7.10.4 was an oversight. We expect to correct this in a forthcoming response to petitions for reconsideration to the ESC final rule. In the meantime, in testing a vehicle under S7.10.4, we would subject a vehicle to the S7.10.2 driving protocol if the telltale is not already extinguished after the engine has been started.
Whether FMVSS No. 126 permits the use of multi-mode ESC controls
You finally asked us to confirm that multi-mode controls are permitted under S5.4 of FMVSS No. 126. You argued that most vehicles are designed with multi-mode controls, which you described as potentially involv[ing] one activation to disable the vehicles traction control system, another activation to alter the ESC algorithm to an intermediate sport mode, another activation to fully disable ESC, and a final activation to restore traction control and ESC to full on. You further argued that these types of controls are widely used by manufacturers and work well for consumers.
S5.4 allows manufacturers to include in their ESC systems either an ESC Off control whose only purpose is to place the ESC system in a mode in which it will no longer satisfy the performance requirements of S5.2.1, S5.2.2 and S5.2.3, or controls for other systems that have an ancillary effect upon ESC operation. The agency made this distinction because of a difference in labeling requirements between the two types of controls. The labeling requirements at issue do not apply until September 1, 2011.
The multi-mode controls you ask about have attributes that overlap the two categories of controls identified in S5.4. We expect to clarify the regulatory text of S5.4 in a forthcoming response to petitions for reconsideration to the ESC final rule.
We confirm, however, that these multi-mode controls are permissible under S5.4. We note that S5.4 also states that Controls of either kind that place the ESC system in a mode in which it will no longer satisfy the performance requirements of S5.2.1, S5.2.2 and S5.2.3 are permitted, provided that the further requirements of S5.4s subparagraphs are met. Therefore, the multi-mode controls would also need to meet the requirements of S5.4.1, S5.4.2, and S5.4.3.
While S5.4.1 applies in the same manner to both categories of controls identified in S5.4, the other two subparagraphs specify different labeling requirements for the two types of controls. Since the multi-mode controls you ask about have attributes that overlap the two categories of control, we would expect to clarify in our response to petitions how the labeling requirements apply to multi-model controls. It is not necessary to resolve that issue in this interpretation since the requirements do not apply before September 1, 2011.
If you have any further questions, please feel free to contact Rebecca Schade of my staff at (202) 366-2992.
Anthony M. Cooke
 E.g., starting the engine, achieving a speed of roughly 48 km/h and making both a left and a right turn within 2 minutes.